Abstract: An absorption spectroscopy device for determining the concentration of a gas (such as oxygen) in a sample cell includes a neutral density absorber or a quarter wave plate. Laser radiation from a laser diode passes through the neutral density absorber or the quarter wave plate, then passes through the sample cell, and then is incident upon a detector. In some embodiments, the laser diode is driven with a drive current having a stepped periodic waveform.

Abstract: The absorption of laser radiation by a gas (such as oxygen and/or carbon dioxide) in human breath is detected on-airway by generating laser radiation using a laser diode, passing the laser radiation through a volume containing human breath multiple times, and detecting the laser radiation which is not absorbed by gases in the volume. To reduce the amount of energy required to control the laser diode, a laser diode is selected which generates laser radiation having a wavelength which is reasonably close to the wavelength of an absorption line of a desired gas when the laser diode is at or near normal body temperature. By passing the laser radiation through the sample gas multiple times, a longer path through the sample gas is provided for absorption thereby allowing the concentration of a gas having weak absorption lines (such as oxygen) to be determined using on-airway absorption detection.

Abstract: A laser diode/lens assembly wherein a lens (or multi-lens assembly) is immovably adhered to a housing of a laser diode package. The laser diode package may be a metal can style package having a substantially transparent window portion through which laser radiation is emitted when a laser diode inside the housing is supplied with current. The lens may be immovably fixed to an outer surface of this window so that a central axis of a beam of laser radiation emerging from the lens has a desired spatial relationship with a reference surface of the housing. An adhesive such as an epoxy adhesive which is cured under exposure to ultraviolet radiation may be used to freeze the lens in place to the window when the lens is correctly positioned. In accordance with some embodiments of the present invention, a lens is positioned in three dimensions (X, Y and Z) and then fixed in three dimensional space with respect to a laser diode housing.

Abstract: A spectroscopy device comprises a laser diode/lens assembly driven by a periodic stepped laser diode drive current. Each period of the stepped laser diode drive current has a plurality of constant current intervals: a left baseline interval, a left skirt interval, a peak interval, a right skirt interval, and a right baseline interval. The left and right skirt constant current intervals are used to lock the laser radiation emitted during the peak interval onto a preselected absorption line. The left and right skirt intervals are also used to obtain a value indicative of line width. The peak interval is used to obtain a value indicative of peak absorbance. Multiplying the peak and line width values together yields a value indicative of a gas concentration which is substantially independent of foreign gas line-broadening effects.

Abstract: A spectroscopy device comprises a laser diode/lens assembly driven by a periodic stepped laser diode drive current. Each period of the stepped laser diode drive current has a plurality of constant current intervals: a left baseline interval, a left skirt interval, a peak interval, a right skirt interval, and a right baseline interval. The left and right skirt constant current intervals are used to lock the laser radiation emitted from the laser diode onto a preselected absorption line. The left and right baseline constant current intervals are used to subtract baseline absorption measurements from peak constant current interval absorption measurements. A high frequency common mode noise rejection circuit rejects noise common to a monitor radiation detector and a radiation detector which detects radiation passing through a sample cell. A serial line locking cell is provided to allow locking when little or no absorbing material is present in the sample cell.